In the coating of the convex side of an optical lens for blocking purposes the prevalent practice is to position the lens on a horizontal support with its convex side facing upward and either brushing or spraying the liquid coating material on the convex side. The brushing operation is more time consuming than spraying and is apt to leave brush marks and a film of uneven thickness whereby after the lens has been deblocked the peeling of the film from the convex side of the lens is difficult and often occurs in pieces and strips at the weak valleys of brush marks or thinner portions of the film. On the other hand, the spraying operation usually is done with an aerosol type spray which, owing to the high percentage of thinner and to overspray or scatter-loss, substantially increases the cost of the delivered film. In addition, the application of a sprayed film whether of the aerosol type or conventional type requires special skill in order to obtain the requisite uniform film thickness free of pinholes, sags, and runs. Aside from the above-mentioned disadvantages and other well known disadvantages of brushing and spraying techniques, the drying time of the brushed or sprayed film may be substantial, i.e. 10 to 15 minutes and if a substantial number of lenses are being coated by spraying, ventilating and overspray catching equipment may be required.
As is well known in the art the coated lens is blocked by casting a low melting point fusible alloy against the coated convex side of the lens, the blocked lens being mounted on the spindle of a machine for grinding and polishing of the uncoated concave side of the blocked lens. Deblocking may be effected as by mechanical jarring of the blocked lens or by "picking off" the blocking alloy from the coated side of the lens.
Examples of other known methods of blocking and deblocking of optical lenses are disclosed in the following U.S. Patents:
Tillyer et al. U.S. Pat. No. 2,224,168, date Dec. 10, 1940 PA0 Canning U.S. Pat. No. 2,352,616, dated July 4, 1944 PA0 Lanman U.S. Pat. No. 3,355,342, dated Nov. 28, 1967 PA0 Cox et al. U.S. Pat. No. 3,404,488, dated Oct. 8, 1968 PA0 Olsen et al. U.S. Pat. No. 4,158,273, dated June 19, 1979